Also spelled Samain or Samonios (On a
Gaulish Coligny Calendar Tablet).
The festival of the dead, swans, mating, marriage {royal}, diving the future and associated with a dozen or so tales of Rhiannon.
Samhain is also when regular mating between the Irish God Dagda and Goddess Morrigan took place.
To confuse the matter of WHEN Samhain actually took place, there was the Roman Festival of Pomona {where the bobbing for apples thing comes into Halloween}; All Hallows, a Christian festival also called Hallowmass and celebrated on Nov 1st ; and then All Saints Day {Nov 2nd}.
{The difference between All Hallows and All Saints? All Hallows celebrated saints and redeemed sinners restored to heaven "now" and upon the judgement of Jesus. All Saints celebrated all of the dead. The vast majority of the hokey, but fun, ghost and goblin stuff involving Halloween came from All Saints Day, not from Samhain.}
Samhain TRADITIONALY was observed on the night and following day exactly between the Autumn Equinox and Midwinter Solstice. {Note, this is a bit further into November. Not on Halloween, at least not for another few hundred years.}
Samhain also was NEVER the beginning or end of the Celtic calendar. {Midsummer or Midwinter was, however, depending upon which calendar you mean...}
Most ritual observances probably had to do with rebuilding Tara {a magical hill. Destroyed every year. I'll node the story soon} symbolic suffering and displays of courage in the name of the kingdom, all sorts of dancing, partying and probably some, ahem, mating. No, I won't node what I do on Samhain.